Variable-Stroke Valve Drive With a Double Leg Spring

ABSTRACT

A variable-stroke valve drive includes a double leg spring with a first spring leg and a second spring leg in a cylinder head of an internal combustion engine and a pivot lever. The pivot lever is supported on a guideway track of a guideway by a rolling element having a pivot point and the pivot lever, by way of a control track, is supported so as to be clearance-free on an intermediate element to a charge-cycle valve. The pivot lever is pivotable by a cam of a cam shaft for adjusting a stroke and the pivot point is displaceable parallel to the guideway track by an adjustment installation for adjusting a stroke height. The double leg spring in a central region forms an intermediate leg. A respective end of the first and second spring legs is formed to be largely parallel to a longitudinal axis of the double leg spring.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a variable-stroke valve drive having a double leg spring in a cylinder head of an internal combustion engine.

A generic double leg spring for a variable-stroke valve drive in a cylinder head of an internal combustion engine is known from the German first and unexamined publication DE 101 22 152 A1, for example. Described in this first and unexamined publication is an assembly aid for a double leg spring for a variable-stroke valve drive in a cylinder head of an internal combustion engine, wherein the double leg spring is embodied by at least one first and one second leg spring which are disposed so as to be largely coaxial to a common spring axis, and the first leg spring has a first spring leg and the second leg spring has a second spring leg, wherein the winding directions of the first and of the second leg spring are mutually opposite, and the first and the second leg spring in the region of the reversal of the winding direction conjointly form a common intermediate leg which is able to be connected to a portion of the cylinder head, wherein the assembly aid, by way of the intermediate leg in a pre-loaded operating position, releasably connects the first and the second spring leg to one another. Risk-free and problem-free assembling of the double leg spring in a variable-stroke valve drive in a cylinder head in an internal combustion engine is possible as a result of the assembly aid.

A variable-stroke valve drive for an internal combustion engine is known from DE 10 2006 033 559 A1. The variable-stroke valve drive for an internal combustion engine has at least one first and one second cylinder and identically acting charge-cycle valves, wherein each cylinder is assigned one charge-cycle valve activation unit. This charge-cycle valve activation unit is composed of at least:

an intermediate lever which is mounted so as to be displaceable on a guideway track of a guideway, on the one hand, and has a working curve, on the other hand, wherein the working curve by way of an intermediate element is operatively connected to a charge-cycle valve, wherein a first actuation device for rotating the intermediate lever, counter to a spring force of a spring element, about a guideway proximal point is provided, wherein the intermediate lever by way of a second actuation device is displaceable along the guideway track, wherein the second actuation device has a first setting point for a zero stroke, at least one second setting point for a partial stroke, and a third setting point for a full stroke of the charge-cycle valve, and wherein the charge-cycle valve of the first cylinder is assigned a first second actuation device, and the charge-cycle valve of the second cylinder is assigned a second second actuation device.

Furthermore known from European patent document EP 2 568 132 B1, from which the present invention proceeds, is a variable-stroke valve drive with a double leg spring in a cylinder head of an internal combustion engine. The valve drive comprises a pivot lever which by way of a rolling element having a pivot point is supported on a guideway track of a guideway, on the one hand, and by way of a control track is supported so as to be clearance-free on an intermediate element to a charge-cycle valve, on the other hand. For adjusting the stroke between the support points, the pivot lever is pivotable, counter to a force of the double leg spring, in a controlled manner by a cam of a cam shaft, on the one hand, and the pivot point by an adjustment installation for adjusting the stroke height is displaceable in a controlled manner parallel to the guideway track, on the other hand. The double leg spring in the central region thereof forms an intermediate leg having a reversal of the rotation direction of the two spring legs, wherein the double leg spring is able to be assembled in the region of the intermediate leg.

The EP patent mentioned last thus describes a variable-stroke valve drive having a double leg spring embodiment with spring legs in an S-bend, wherein the spring leg engages on the contact face on the pivot lever from “above” and when assembling has to be introduced into the lateral guide tabs of the pivot lever from “the rear”.

This results in the following issues:

1. As a result of the S-bend of the spring legs the rotation angle of the eccentric shaft, the adjustment element, is geometrically restricted to 254°, because the spring leg will otherwise collide with the eccentric of the eccentric shaft.

2. As a result of an assembly error one or both legs of the spring legs may not be correctly introduced onto the contact face of the pivot lever, but bear laterally on the end faces of the lateral guide tabs. During the first revolution of the cam shaft, and thus a pivoting movement of the intermediate lever, the spring leg slides down laterally from the intermediate lever and then rubs on the cam shaft. The variable stroke function of the variable-stroke valve drive is thus no longer guaranteed. This leads to wear on the cam shaft tube by the spring leg, and the cam shaft may break.

It is an object of the present invention to avoid the abovementioned issues.

According to the invention, the contact of the spring legs of the double leg spring is modified, from a vertical arrangement (S-bend) to a horizontal arrangement.

This results in the following advantages:

1. As a result of the design embodiment according to the invention, the spacing of the spring leg, in the region of the intermediate lever, from the eccentric, the adjustment element, is significantly enlarged, thus making possible an enlargement of the rotation angle of the eccentric shaft (up to 300°). As a result, there is a larger adjustment angle available for designing the stroke function of the variable-stroke valve drive. A larger eccentric stroke can thus be implemented without enlarging the adjustment torque of the variable-stroke valve drive (in which case a stronger adjustment motor would be required).

2. Furthermore, the design embodiment according to the invention leads to improved assembling. The L-shaped spring leg of the double leg spring needs only to be placed on the corresponding contact face of the intermediate lever. Advantageously, no additional positioning of the spring leg is required, thus ruling out any assembly error.

The invention will be explained in more detail hereunder in one figure by means of the prior art and in two figures by means of a design embodiment according to the invention in comparison to the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a portion of a generic variable-stroke valve drive according to the prior art;

FIG. 2 shows a lateral view of a variable-stroke valve drive according to the invention in comparison to the prior art; and

FIG. 3 shows a perspective view of the variable-stroke valve drive according to the invention in comparison to the prior art.

DETAILED DESCRIPTION OF THE DRAWINGS

The same reference signs apply hereunder to identical construction elements in FIGS. 1 to 3 .

FIG. 1 shows a perspective view of a portion of a generic variable-stroke valve drive 1 with a double leg spring 2 according to the prior art. The portion is provided for two charge-cycle valves 9, wherein only one charge-cycle valve 9 is provided with a reference sign. This valve drive 1 can be installed in a cylinder head of an internal combustion engine (not illustrated) and is known from the prior art, i.e., DE 10 2006 033 559 A1.

The valve drive 1 comprises a pivot lever 3 which by way of a rolling element 4 having a pivot point is supported on a guideway track 5 of a guideway 6, on the one hand, and by way of a control track 7 is supported so as to be clearance-free on an intermediate element 8, a roller cam follower, to a charge-cycle valve 9, on the other hand. In order to be supported without any clearance, the intermediate element 8 in relation to the charge-cycle valve 9 is supported on a clearance compensation element 14, preferably a hydraulic clearance compensation element 14. In order for the stroke to be adjusted, the pivot lever 3, counter to a force of the double leg spring 2, is pivotable in a controlled manner between the support points of a cam (not illustrated) of a camshaft, on the one hand, and the pivot point of an adjustment installation 10, an eccentric shaft, for adjusting the stroke height is displaceable in a controlled manner parallel to the guideway track 5, on the other hand. Furthermore, the double leg spring 2 in the central region thereof forms an intermediate leg 11 having a reversal of the rotation direction of the two spring legs 2 a, 2 b (2 b is not provided with the reference sign due to being invisible), wherein the intermediate leg 11 is encased by a sheet-metal assembly plate. Using an assembling means, the double leg spring 2 is able to be fastened either to the cylinder head or to a shaft bearing (not illustrated). In terms of the functional mode of the variable-stroke valve drive 1 reference is also made to international patent application WO 02/092972 A1.

As has already been illustrated, the known double leg spring embodiment has spring legs 2 a, 2 b with an S-bend, wherein the spring legs 2 a, 2 b engage on the contact faces on the pivot lever 3 from “above” and when assembling are introduced into lateral guide tabs (not provided with a reference sign) of the pivot lever 3 from “the rear”.

FIG. 2 shows a lateral view of a variable-stroke valve drive 1 according to the invention in comparison to the prior art. The same circumstances apply to FIG. 2 as to FIG. 1 . The spring leg 2 a which is at the bottom in the drawing corresponds to the embodiment according to the prior art; the spring leg 2 b which is at the top in the drawing corresponds to the design embodiment according to the invention. According to the invention, the end of the spring leg 2 b in this comparison is formed so as to be largely parallel to a longitudinal axis 12 of the double leg spring 2.

In the present exemplary embodiment, the spring leg 2 b is formed toward the inside. In a further exemplary embodiment, the spring leg 2 b may also be formed toward the outside.

Furthermore, the spring leg 2 b in the present exemplary embodiment is formed by approx. 90°, larger or smaller forming angles also being possible here.

In order for the spring leg 2 b to bear in the best possible manner, the pivot lever 3 for each end of the spring legs 2 a, 2 b according to the invention has one corresponding contact face 13.

FIG. 3 shows a perspective view of the variable-stroke valve drive 1 according to the invention in comparison to the prior art. The same as has been discussed in the context of FIG. 2 applies. Finally, it is to be mentioned that both spring legs 2 a, 2 b of the double leg spring 2 in reality—and as opposed to FIGS. 2 and 3 -have the L-shape, and the pivot lever 3 has one contact face 13 for each spring leg 2 a, 2 b.

The following advantages are derived by virtue of the design embodiment according to the invention:

1. The spacing of the spring leg 2 b in the region of the intermediate lever 3 from the eccentric, the adjustment element 10, is significantly enlarged, thus making possible an enlargement of the rotation angle of the eccentric shaft (up to 300°). As a result, there is a larger adjustment angle available for designing the stroke function of the variable-stroke valve drive 1. A larger eccentric stroke can thus be implemented without enlarging the adjustment torque of the variable-stroke valve drive 1.

2. Furthermore, the design embodiment according to the invention leads to improved assembling. The L-shaped spring leg 2 b of the double leg spring 2 needs only to be placed on the corresponding contact face 13 of the intermediate lever 3. Advantageously, no additional positioning of the spring leg 2 b is required, thus ruling out any assembly error.

LIST OF REFERENCE CHARACTERS

-   1 Valve drive -   2 Double leg spring -   2 a Spring leg according to the prior art -   2 b Spring leg according to the invention -   3 Pivot lever -   4 Rolling element -   5 Guideway track -   6 Guideway -   7 Control track -   8 Intermediate element -   9 Charge-cycle valve -   10 Adjustment installation -   11 Intermediate leg -   12 Longitudinal axis -   13 Contact face -   14 Clearance compensation element 

1.-4. (canceled)
 5. A variable-stroke valve drive, comprising: a double leg spring with a first spring leg and a second spring leg in a cylinder head of an internal combustion engine; and a pivot lever, wherein the pivot lever is supported on a guideway track of a guideway by a rolling element having a pivot point, wherein the pivot lever by way of a control track is supported so as to be clearance-free on an intermediate element to a charge-cycle valve, wherein the pivot lever is pivotable, counter to a force of the double leg spring, in a controlled manner by a cam of a cam shaft for adjusting a stroke, and wherein the pivot point is displaceable in a controlled manner parallel to the guideway track by an adjustment installation for adjusting a stroke height; wherein the double leg spring in a central region of the double leg spring forms an intermediate leg having a reversal of a rotation direction of the first and second spring legs and wherein the double leg spring is able to be assembled in a region of the intermediate leg; wherein a respective end of the first and second spring legs is formed to be largely parallel to a longitudinal axis of the double leg spring.
 6. The variable-stroke valve drive according to claim 5, wherein the respective end of the first and second spring legs is formed toward an inside or an outside of the variable-stroke valve drive.
 7. The variable-stroke valve drive according to claim 5, wherein the respective end of the first and second spring legs is bent approximately 90° with respect to the respective first and second spring leg.
 8. The variable-stroke valve drive according to claim 5, wherein the pivot lever has a respective contact face for the respective end of the first and second spring legs. 